I have similar problems in my place, older home but newer windows, it's usually ok until it gets down below -25, at that point condensation starts to build up and then freeze. I don't know if everyone has this problem, our neighbors just put in brand new windows and they have the same problem.. so I have a feeling it's something we just have to live with to enjoy this great weather..
Couple of things to keep in mind.. you need to keep a close eye on your humidifier and turn it down as the temp drops.. there are charts online that show the temperature and what the indoor humidity should be. Something else you may want to try is to put the shrink wrap plastic weather proofing stuff, I did this on a few windows as a test and it seems to have worked.. got the 3M kit from crappy tire.. I still get a bit of condensation (behind the blackout blinds in the bedroom) but it doesn't freeze and is easy to wipe off..